Fixes a couple of bugs from the introduction of TestNode:
- test scripts were no longer able to specify a custom timeout for
starting a node. Therefore tests with nodes that take a long time to
start up (eg pruning.py) would fail.
- the test for whether a node has failed on start up was broken
by changing 'assert x is None' to 'assert not x'. Since
subprocess.poll() can return None (indicating the node is still running)
or 0 (indicating the node exited with return code 0), this was a
regression.
When running the tests locally with a parallelism of 4 on an otherwise
busy system, RPC can take quite a wait to come up.
Change the timeout to 60 seconds just to be safe.
TestNode is a class responsible for all state related to a bitcoind node
under test. It stores local state, is responsible for tracking the
bitcoind process and delegates unrecognised messages to the RPC
connection.
This commit changes start_nodes and stop_nodes to start and stop the
bitcoind nodes in parallel, making test setup and teardown much faster.
